It is important to downsize appearance of a mobile radio device such as a cellular phone, a smartphone, and a mobile router. Many of such mobile radio devices each have an antenna for communication built in a housing.
Dimensions of each antenna element in the antennas may be set to be shorter than a wavelength corresponding to a resonance frequency so that the antenna can be built within dimensions of a housing, which may cause deterioration in antenna performance due to reduction in the dimensions of each antenna element.
Accordingly, in order to ensure communication performance, particularly, at a location where a radio wave environment is poor and the like, an external antenna a length of which is not reduced with respect to the wavelength corresponding to the resonance frequency may be used instead of the built-in antenna with a reduced length, to thereby enhance antenna performance.
Then, as a configuration described in PTL 1, there is a configuration in which an external antenna is placed on a cradle (also referred to as a desktop holder, which also serves as a charging station) of a radio device.
FIG. 36 illustrates an example of a cradle 160 on which an external antenna 161 is placed, and an example of a radio device 150 placed on the cradle 160.
Note that PTLs 2 to 6 disclose techniques for improving performance of an antenna.